Recent advances in plant genetic engineering have enabled the engineering of plants having improved characteristics or traits, such as disease resistance, insect resistance, herbicide resistance, enhanced stability or shelf-life of the ultimate consumer product obtained from the plants and improvement of the nutritional quality of the edible portions of the plant. Thus, one or more desired genes from a source different than the plant, but engineered to impart different or improved characteristics or qualities, can be incorporated into the plant's genome. One or more new genes can then be expressed in the plant cell to exhibit the desired phenotype such as a new trait or characteristic.
An inducible promoter is a promoter that is capable of directly or indirectly activating transcription of one or more DNA sequences or genes in response to an inducer. In the absence of an inducer, the DNA sequences or genes will not be transcribed. The inducer can be a chemical agent, such as a metabolite, growth regulator, herbicide or phenolic compound, or a physiological stress directly imposed upon the plant such as cold, heat, drought, flooding, salt or toxins.
Environmental stresses cause billions of dollars of economic losses to crops and forest by yield and quality losses. Globally, the most commonly encountered environmental stresses are heat stress due to high temperature, freeze or chilly stress due to low temperature, drought due to water shortage and flooding due to excessive water. A limited number of genetically engineered crops and trees have been or under field tests for commercial release, for example, drought-tolerant maize by Monsanto and cold hardy Eucalyptus tree by ArborGen. Many currently used stress-tolerance genes are more specific to one stress, such as DHS for drought tolerance, and CBF2 for cold hardiness, and engineering these genes under constitutive promoter (universally expressing) can cause abnormal phenotypes because many of these genes are developmentally regulated. Therefore, it would be highly desirable to express these stress-tolerance genes only when stresses are upon to plants, and this can be done by use of tightly regulated, stress-inducible promoters.